The present invention relates to an image processing apparatus and, particularly, to a configuration of an image processing apparatus which generates an interpolated image by means of image compression processing in which an image is compressed for data amount reduction.
In image processing applications, it is required to process large amounts of data such as voice and video. To reduce data amounts when performing transfer of and storing of such image data into memory, image compression processing is performed. For image compression processing, a frame memory is generally used as a working area and image data of one or more frames are stored into this frame memory.
Meanwhile, along with recent trends toward visualizing higher definition images, for example, a full HD (High Definition image (High Vision image) with 1920×1080 pixels), there is a need for a double speed display or the like providing a higher image quality, which in turn increases the processing load. On the other hand, from a viewpoint of cost or the like, the storage capacity and bandwidth of a frame memory are finite and the processing speed and capacity of an operational processing device are limited. For efficient processing, it is hence required to distribute individual processes among limited resources.
For instance, the above-mentioned double speed technique is used to improve the response performance of a liquid crystal panel. The double speed technique multiples the number of frames by executing frame interpolation which generates another frame image from a plurality of frames. This technique multiplies the number of frames to be displayed on the liquid crystal panel and shortens a hold time which is intrinsic to the liquid crystal panel (the time during which a single frame image remains displayed thereon). Thus, the double speed technique suppresses a sense of persistence of vision and improves the response performance (Moving Picture Response Time: MPRT).
The frame interpolation in the case of double speed processing generates an intermediate image as an interpolated frame from two temporally successive frame images. It is needed to generate this interpolated frame within one vertical period (V). For high definition images having a very great number of pixels, it is thus required to increase the storage capacity and bandwidth of a frame memory. However, the bandwidth between the frame memory and its bus is system-specific. To increase an effective bandwidth, it becomes necessary to reduce the apparent amount of data. To reduce this amount of data, compression/decompression (expansion) processing is carried out. In the compression/decompression (expansion) processing, an adaptive compression may be performed which selectively use a compression processing scheme (algorithm) such as a compression rate depending on image features to achieve efficient image compression processing and thus to minimize degradation of image equality.
The amount of compressed data varies depending on the feature of the compressed image. After compression of, e.g., an image of a high granularity picture, the amount of the compressed data is greater, whereas, image compression of a white wall-like picture with less high range components produces a smaller amount of compressed data. In a case that the amount of compressed image data is very large, a situation may occur that compressed image data cannot be stored into a memory within a fixed processing period (vertical period). As a method for avoiding such situation, Patent Document 1 (Japanese Unexamined Patent Publication No. Hei 9 (1997)-214957) describes an configuration in which a process of estimating the amount of data after being compressed per field is performed. In the configuration described in Patent Document 1, before compression processing, image data is pre-scanned to determine its amount of data. According to this amount of data, quantized coefficients and encoding are configured so that compressed data will fall within a target data size, and an adaptive compression per field is performed.
[Patent Document 1]
Japanese Unexamined Patent Publication No. Hei 9 (1997)-214957